Maximum thermometer.



No. 695,262. Patented Mar. ll, I902.

G. H. ZEAL.

MAXIMUM THERMUMETER.

(Application filed Oct. 30, 100i.

(No Model.)

IlrrrTnn STATres PATENT @rrrcn.

GILES II. ZEAL, OF LONDON, ENGLAND.

MAXIMUM THERMOMETER.

SPEGIFICA'JIION forming part of Letters Patent No. 695,262, dated March11, 1902.

Application filed October 30, 1901. Serial No. 80,544. (No model.)

tain new and useful Improvements in Maximum Thermometers, of which thefollowing is a full, clear, and exact description, and for V which Ihave made application for patent in Great Britain dated the 1st day ofOctober,

In clinical and other maximum thermometers as formerly constructed adifficulty is experienced in returningthe indicatingcolumn or index toits normal position. Attempts have been made to remedy thisinconvenience by the provision of a body of air in a chamber at theupper end of the tube closed by a flexible diaphragm, of india-rubber orthe like, acted upon by a piston or plunger or by the finger. It hasalso been proposed to form an air-chamber of glass at the upper end ofthe tube and to hermetically seal such chamber by the blowpipe. Withthis latter form it was necessary to use heat to expand the air withinthe chamber to cause it to exert a pressure on the indicating column orindex to return the latter to its normal position. These attempts,however, have not been entirely satisfactory, as the comparatively largebody of air contained in the chamber at the upper end of the tube and inthe tube itself causes oxi-.

dation of the mercury and leads to errors of indication, in addition towhich such air is liable to be expanded unduly by heat, and thus exert apressure on the indicating column or index of mercury when not required.According to my invention I overcome these inconveniences in thefollowing manner and as represented in the accompanying drawings asapplied to a clinical thermometer, in which- Figure 1 is a longitudinalsection of my improved thermometer, showing the instrument in its normalcondition and ready for taking a temperature. Fig. 2 is a similarsection showing the instrument as it would be when aftera temperaturehas been taken and noted the indicating column or index is being returned below the scale in readiness for a11- other temperature to betaken. Fig. 3 is an elevation of the upper part of the thermometor drawnat right angles to Figs. 1 and 2.

Fig. 4 is a longitudinal section of the upper part of a thermometer,showing a slight modification; and Fig. 5 is a longitudinal section ofthe lower part of a thermometer, showing another modification.

According to my invention I form by means of a blow-pipe and attach tothe upper end of the thermometer-tube a a compressible glass chamber 1),which I supply with mercury and seal by means of the blowpipe. Below thecompressible chamber Z) I form a smaller chainher 0 by expanding thebore of the tube a. for

the purpose of receiving any mercury which may be caused to leave thecompressible chamber I) through the action of heat.

(Z is the ordinary constriction of the bore to cut off a portion of themercurial column to form a maximum index, (but other methods ofobtaining a maximum index may be used,) and e is an ordinarymercury-bulb.

The compressible chamber b maybe of any suitable shape, that shown atFigs. 1, 2, 3

being preferred, in which case the chamber 1) is compressed by the thumband finger. When, however, such a form as that shown at Fig. 4 isadopted, the thermometer may be held in the hand and a single fingerused to press on the top of the chamber 12.

In some cases I form, just above the constriction cl, a small chamber fby expanding the bore of the tube a, so that in the event of theobserver forcing the mercury in the chamber b farther than necessary theexcess of mercury shall accumulate in such chamber f and not follow theindex past the constriction d.

I would here remark that a small quantity of a gaseous body isintroduced into the thermometer between the two bodies of mercury tokeep them apart, as shown at g in Fig. 2.

By my improved thermometer after the indicating column or index hasrisen to the maximum it may after observation be returned to its normalposition by applying pressure to the elastic portion of the compressiblechamber 1). A

After taking a temperature themercurial column which formed the maximumindex need onlybe forced down until the top thereof is below the scale,after which the contraction of the mercury in the bulb e by reduction oftemperature may leave a vacant space in the bore below the constrictiond and a portion of the mercury which formed the maximum scale above saidrestriction, as shown in Fig. 1, as in the common mode of using maximumthermometers. When a temperature is to be taken, the mercury in the bulbexpands, as is Well known, rises into contact with the small quantity ofmercury above the constriction d, and raises it to the maximum degree toform an index. Then by compressing the chamber 1) mercury therefrom isforced into the bore and acts upon the index to return the latter belowthe scale, the two bodies of mercury being kept apart 'by the gaseousbody 9 between them. After this on relieving the chamber 1) frompressure this expands and the mercury in the bore above the gaseous body9 returns to said chamber b.

What I claim as my invention, and desire to secure by Letters Patent, is

1. A maximum thermometer having a compressible glass chamber at itsupper end charged with mercury and sealed by the blowpipe, substantiallyas herein set forth and for the purpose stated.

2. In a maximum thermometer having a mercury-bulb, a tube communicatingtherewith, and means for registering the maximum temperature in saidtube, the combination therewith of a compressible glass chamber at theupper end of the tube and communicating therewith, a charge ofmercury'in said compressible chamber, and a small quantity of a gaseousbody between the two bodies of mercury, substantially as herein setforth.

3. In a maximum thermometer having a mercury-bulb, a tube communicatingtherewith, and means for registering the maximum temperature in saidtube, the combination therewith of a compressible glass chamber at theupper end of the tube and communicating therewith, a charge of mercuryin said compressible chamber, a small quantity of a gaseous body betweenthe two bodies of mercury,

and a small chamber or enlargement in the bore of the tube just belowthe compressible ous body between the two bodies of mercury,

a small chamber or enlargement in the bore of the tube just below thecompressible chamber, and another small chamber or enlargement in thebore of the tube a little above the constriction, substantially asherein set forth.

5. In a maximum thermometer having a mercury-bulb, a tube communicatingtherewith, and means for registering the maximum temperature in saidtube, the combination therewith of a compressible glass chamber at theupper end of the tube and communicating therewith, a charge of mercuryin said compressible chamber, a small quantity of a gaseous body betweenthe two bodies of mercury,-

and a small chamber or enlargement of the tube a little above theconstriction, substantially as herein set forth.

In testimony whereof I afflx my signature in presence of two witnesses.

G. H. ZEAL. YVitnesses:

B. J. B. MILLS, CLAUDE K. MILLS.

